The present invention relates to an apparatus for making profiled plastic tube by means of an extruder, said apparatus comprising two opposite circulating chains, each making a plurality of mold halves move along with the tube coming from the extruder, these mold halves together constituting, in a rectilinear portion of the paths of said chains, a mold cavity in which the tube is being given its profile.
To the extent that production speeds are being increased, more severe requirements hold for the drive of the chain which supports the mold halves. More particularly, in that case, a perfectly regular course of the series of adjoining mold halves over the effective portion of the path will be necessary. Generally speaking, certain minor irregularities in said course will be caused by play in the links of the drive chain and by irregularities, particularly differences in size, in the individual molds.
In this connection it is important that the cylindrical cavity of molds which, in the common, rectilinear portion of the path is effective to operate upon the tube, is kept undisturbed as good as possible. This is so for the full length of said cavity, but the problem requires particular attention at the beginning and at the end of the path, so at the entrance and the exit ends. Irregularities in the course of the moving molds has, so far, been one limitation on the production speed as far as standards of quality of the product were to be met.